Ellipsometric and reflectance measurements were made with magneto-optically self-nulling ellipsometer on the iron surface being passivated. The passivation was induced by abruptly changing potential of the mechanically polished high purity iron from the reduction potential to the oxidation potential in basic solutions. From the differences in the optical paramates(${Delta},;{psi}$) and reflectance (R) between the reduced (film-free) and oxidized (film-covered) states, the thickness(${ au}$) and optical constants (n, k) of the film in the early stage of its formation were computed as functions of pH and time. From the computed values, it was deduced that the properties of the anodic film did not undergo a drastic change with time which would indicate a transformation of the film before effective passivity is attained, and that the film reached its stady state within a few second. The thickness of anodic film was $14;{sim};23{AA}$. The anodic films also seemed to have small values of optical absorption coefficient. The film formed in high pH environments had thinner and denser structure than that formed in low pH.